This invention relates to hydraulic fluid systems for a motor vehicle automatic power transmission. More particularly, it pertains to draining oil automatically from an oil cooler and fluid supply lines to a transmission sump.
Generally, automatic transmission fluid for operating and lubricating an automatic transmission is contained in an oil reservoir such as oil pan and the like located at the underside of the automatic transmission case. The automatic transmission fluid contained in the oil pan is inducted by an oil pump and is supplied to a torque converter, miscellaneous lubrication circuits, and a hydraulic control system, which produces various magnitudes of pressure and provides circuit paths between the pressure sources and the appropriate components that employ the pressure to perform their functions.
For example, the various speed ratios produced by the transmission result by selectively engaging and disengaging various friction elements, hydraulically actuated clutches and brakes. The applied and released condition of the friction elements operate to interconnect and disconnect elements of the planetary gearsets in order to produce multiple forward drive gear ratios and reverse drive. The friction elements are applied and released in response to the pressurized and vented state of a hydraulic servo through which the friction elements are actuated.
The magnitude of torque transmitted by the various friction elements in the several gear ratios is reflected in the magnitude of pressure applied to each friction element. When the magnitude of transmitted torque is high, the magnitude of actuating pressure is high. Generally, during operation in the lowest forward drive gears and reverse gear, the transmitted torque magnitude is high. A control system for an automatic transmission produces line pressure up to about 300 psi. The lubrication circuit is continually supplied with fluid during normal operation, and typically fluid is present in the cooler and its supply lines even after the pump is stopped by turning off the vehicle's engine.
Under operating conditions when the automatic transmission fluid is at its normal, elevated temperature, fluid from the control system directed to the lubrication circuits passes first through an oil cooler, a heat exchanger usually incorporated in the radiator, where an exchange of heat from the transmission fluid to ambient air or other fluid occurs. The lubrication circuits are supplied from the cooler outlet. Fluid used to lubricate various friction surfaces throughout the transmission returns by gravity to the reservoir, from which it is inducted at the pump inlet.
The cooler is connected to the transmission control system by hydraulic lines, which extend from the transmission case through hydraulic fittings, which connect the lines to the cooler. The cooler is located in the engine compartment in the vicinity of the air inlet shroud, cooling fan, and radiator. The cooler fittings are located above the fittings that connect the lines to the transmission case. The transmission oil pan or reservoir are located at an elevation that is lower than that of the cooler.
Because the cooler lines remain full when the engine is not running, whenever the transmission is disconnected from the cooler supply lines, or the lines are disconnected at the fittings from the cooler, transmission fluid contained in the cooler and lines can pour out into the service area or onto equipment in the engine compartment. To prevent this oil spillage when servicing the transmission, either a catch basin is used to hold the fluid in the lines and cooler when opening the hydraulic fittings at the cooler lines, or the fittings are immediately plugged after disconnecting the lines from the cooler.
There is a need, therefore, for a reliable, low cost technique to prevent spillage and outflow of transmission fluid in this way while servicing the transmission, radiator, or cooler.